Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110;
CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, Universidade do Porto, 4485-661 Vairão, Portugal.
Proc Natl Acad Sci U S A. 2017 May 16;114(20):5219-5224. doi: 10.1073/pnas.1700751114. Epub 2017 May 2.
Yellow, orange, and red coloration is a fundamental aspect of avian diversity and serves as an important signal in mate choice and aggressive interactions. This coloration is often produced through the deposition of diet-derived carotenoid pigments, yet the mechanisms of carotenoid uptake and transport are not well-understood. The white recessive breed of the common canary (), which carries an autosomal recessive mutation that renders its plumage pure white, provides a unique opportunity to investigate mechanisms of carotenoid coloration. We carried out detailed genomic and biochemical analyses comparing the white recessive with yellow and red breeds of canaries. Biochemical analysis revealed that carotenoids are absent or at very low concentrations in feathers and several tissues of white recessive canaries, consistent with a genetic defect in carotenoid uptake. Using a combination of genetic mapping approaches, we show that the allele is due to a splice donor site mutation in the scavenger receptor B1 (; also known as ) gene. This mutation results in abnormal splicing, with the most abundant transcript lacking exon 4. Through functional assays, we further demonstrate that wild-type SCARB1 promotes cellular uptake of carotenoids but that this function is lost in the predominant mutant isoform in white recessive canaries. Our results indicate that SCARB1 is an essential mediator of the expression of carotenoid-based coloration in birds, and suggest a potential link between visual displays and lipid metabolism.
黄色、橙色和红色的着色是鸟类多样性的一个基本方面，也是在配偶选择和攻击性相互作用中重要的信号。这种着色通常是通过饮食中衍生的类胡萝卜素色素的沉积产生的，但类胡萝卜素的摄取和运输机制尚不清楚。普通金丝雀（）的白色隐性品种携带一种常染色体隐性突变，使其羽毛呈现纯白色，这为研究类胡萝卜素着色的机制提供了一个独特的机会。我们进行了详细的基因组和生化分析，比较了白色隐性品种与黄色和红色品种的金丝雀。生化分析表明，类胡萝卜素在白色隐性金丝雀的羽毛和几种组织中不存在或浓度非常低，这与类胡萝卜素摄取的遗传缺陷一致。我们使用了一系列遗传图谱绘制方法，表明 等位基因是由于清道夫受体 B1 （也称为 ）基因的剪接供体位点突变所致。这种突变导致异常剪接，最丰富的转录本缺乏外显子 4。通过功能测定，我们进一步证明野生型 SCARB1 促进细胞摄取类胡萝卜素，但在白色隐性金丝雀中主要的突变同工型中失去了这种功能。我们的结果表明，SCARB1 是鸟类中基于类胡萝卜素的着色表达的重要介质，并提示视觉表现与脂质代谢之间可能存在联系。
